Numerous devices have been developed for handling electrostatic discharge (ESD) events. In the case of NMOS devices the ESD clamps fall into two groups: the active clamps that work in normal operating mode, and the snapback devices which are designed to be triggered and operate in snapback mode during an ESD event and then turn off again as voltage drops below the holding voltage of the device.
The present invention deals with active clamp NMOS devices. These are typically larger than snapback devices but have the advantage of being usable as self-protecting devices, where they are functional even during non-ESD situations. While these devices typically are meant not to go into snapback, local overstresses due to current crowding can cause these devices to go into snapback, thereby damaging the device.
The present invention seeks to reduce such snapback in active NMOS clamps.